1. Field of the Invention:
This invention relates to a functional device using a resonant tunneling effect, and more particularly to a structure of the device applicable to a variety of function circuits.
2. Description of the Related Arts:
Heretofore, high-speed operation in integrated circuits has been improved by miniaturizing circuit elements in the integrated circuits in order to have a transmission time of about 10 pico-seconds. The miniaturization for decreasing the transmission time has almost reached a limit. On the contrary, the time delay due to wirings becomes relatively serious for further improvement of high-speed operation. Thus, there is a new trend that functional devices are used for decreasing the number of wirings and for shortening a total delay time to achieve improved high-speed operation.
A.R. Bonnefoi et al. proposed a resonant-tunneling transistor in "IEEE ELECTRON DEVICE LETTERS" vol. EDL-6, No. 12 (December 1985) pages 636 to 638. The transistor is an MESFET having a resonant-tunneling diode in its source electrode region. A negative differential resistance appears in a current flowing between drain and source electrodes and is controlled by a gate voltage.
This MESFET is constructed of compound semiconductors of GaAs and AlGaAs to achieve a high-speed operation in microwave and millimeter-wave regions. Furthermore, since the MESFET shows negative differential resistance, it has multiple applications such as high-speed digital circuits, tunable millimeter-wave oscillators and negative resistance amplifiers.
Although this MESFET is a functional device presenting a negative differential resistance, many elements and wirings are required for forming circuits such as flip-flops, frequency multipliers and logic circuits. The wirings deteriorate the high-speed operation to prolong the delay time.